Diagnostic method for manufacturing processes

ABSTRACT

A method for use in a system for diagnosing the causes of manufacturing defects involves process characterization. A set of forms is identified for a workpiece and for a piece of manufacturing equipment that acts upon the workpiece. The forms for the workpiece are preferably a hierarchic set of geometric forms. Each such geometric form corresponds to an aspect of the action of the manufacturing equipment upon the workpiece. A plurality of measurements is made on a defective workpiece following the hierarchical order of forms. The measurements are compared to a reference datum, and a deviation from the datum is computed. If the deviation exceeds a preselected threshold, an alert condition results, attributable to the action of the manufacturing equipment. Targeted adjustment corresponding to the action that caused the defect can then be made to the equipment.

FIELD OF THE INVENTION

[0001] The invention relates to diagnostic analysis and, moreparticularly, to the diagnosis of manufacturing defects.

BACKGROUND OF THE INVENTION

[0002] Manufacturing processes, and the products they create, sometimessuffer from defects. The job of detecting and eliminating these defectsfalls to manufacturing engineers, who, over the years, have developedstatistical approaches in an attempt to address them. They have alsodeveloped various controls, ranging from process control to qualitycontrol to product control, for attempting to capture defective productsbefore they reach customers.

[0003] These controls are based on identification of limits on thecapabilities of the various processes that are used in the manufactureof a workpiece or product. For example, process control is based on thecapability of the process that produces the workpiece. An illustrationis provided in FIGS. 1a and 1 b, where shaft 10, produced on a lathe,has a nominal diameter 20, and a sampling of shafts has a distributionof diameters 30 at frequencies 40. The specified tolerance on thediameter dimension is identified by reference numeral 60 as shown inFIG. 1b. The range of the capability of the lathe is shown by numeral50, where the capability may exceed that of the range of the specifiedtolerance. Shafts may have diameters exceeding the upper specificationlevel (USL) 70, while others may have diameters below that of the lowerspecification level (LSL) 80 as shown in FIG. 1b. Parts that exceed thespecifications, according to a quality control approach, would berejected.

[0004] So-called quality control procedures are directed to preventing“out-of-spec” parts reaching customers, but they do not necessarilyreduce the number of rejects. Rather, these approaches seek todistinguish good parts from bad based on product features that appear tobe readily measured, without revealing mechanisms responsible forproduct defects or physical insights that could more readily lead to thediscovery of such mechanisms.

SUMMARY OF THE INVENTION

[0005] The present invention provides approaches for identifying thecauses of manufacturing problems by breaking down the different phasesof a manufacturing process, such as the different actions of a machinetool on a workpiece, so that each phase or action can be related to theformation of an element or a feature of the final workpiece, preferablyproviding a one-to-one correspondence between the forming of the shapeof the feature and a process step or action that produces the shape.This procedure, then, helps reveal defects which process action producesit. Once the source of the defect is detected, both the source and theworkpiece defect it causes can be addressed.

[0006] The present invention provides not only a method for detectingdefects in a manufacturing process, but also a method for identifyingwhere in the process the defects occur, so that appropriate correctiveaction can be identified, and such action taken, at the point ofoccurrence. This object is accomplished by relying on a processcharacterization approach that focuses on the actual effect of theprocess on a workpiece.

[0007] In one embodiment of an aspect of the present invention, a methodfor use in a system for diagnosing the causes of deviation from anintended form in a workpiece produced by a manufacturing process isprovided. At least one form is defined for the workpiece and for a pieceof manufacturing equipment that acts upon the workpiece to impart theform. A plurality of measurements for each workpiece is defined, eachrelative to a respective reference datum. The subsequent steps involvegenerating a record of the plurality of measurements corresponding toeach workpiece and inferring from the comparison of the measurements forat least one of the workpieces the existence of an alert conditionassociated with the action of the manufacturing equipment on theworkpiece.

[0008] Another embodiment of an aspect of the present invention involvesa method for identifying evidence of deviation from specification in aworkpiece produced by a manufacturing process, the manufacturing processbeing performed by respective manufacturing equipment. The methodincludes identifying a set of repeated portions of the workpiece, eachinstance of a repeated portion having forms, the form of one instance ofa repeated portion being substantially the same form as the otherinstances. For each instance of the repeated portion, a set ofmeasurements of the reproducible part is made relative to a respectivereference datum. Each set of measurements is compared to a respectivetarget range of values. Based on the comparison, the existence ofevidence of deviation from specification is inferred.

[0009] In still another embodiment of the present invention, a methodfor assessing a condition of a workpiece acted upon by manufacturingequipment starts by identifying a set of forms, each form correspondingto an aspect of the action of the manufacturing equipment upon theworkpiece. The subsequent steps involve making a plurality ofmeasurements for each form; computing, for each plurality ofmeasurements, a respective deviation from a corresponding referencedatum; defining a deviation threshold; and, if a computed deviationexceeds the deviation threshold, inferring the existence of thecondition attributable to the action of the manufacturing equipment onthe workpiece.

[0010] In yet another embodiment of an aspect of the present invention,a method is provided for detecting deviations from an intended form in amechanical part. The deviations are detected on the basis ofmeasurements of geometric properties relative to a reference datum, thegeometric properties imparted by a machine tool operating on themechanical part. The method comprises the steps of: identifying ahierarchic set of geometric forms characterizing the mechanical part,each form corresponding to an action of the machine tool on the part;categorizing the geometric forms from a lowest order to a highest order;making a plurality of measurements corresponding to the lowest orderform; for each plurality of measurements, computing a respectivedeviation from a defining datum; checking for an alert condition foreach of the respective deviations; and if an alert condition is present,inferring a deviation from the intended form.

[0011] In another embodiment of an aspect of the present invention, amethod is provided for characterizing the ability of a machine tool toreproduce a product without deviating from a specification intended forat least a portion of the product, the characterization based upontaking geometric measurements. The method involves identifying a set ofgeometric forms present in the product; selecting a first of the set ofgeometric forms; making a plurality of measurements corresponding to theselected geometric form; for each plurality of measurements, computing adeviation from a respective reference datum; checking for an alertcondition for each of the respective deviations; if an alert conditionis present, adjusting the machine tool and repeating the method from thestep of making additional measurements corresponding to the sameselected geometric form iteratively until no further alert condition isfound. If no alert condition is present, the method is repeated from thestep of selecting the next set of geometric forms by incrementing to thenext form until all geometric forms have been selected and no furtheralert condition is found.

[0012] The present invention also provides a method for representingmeasured deviations for features attributable to the forming of aphysical object, in a suitable frame of reference. The method involvesidentifying an order for the features; providing a first region forcomparing measurements corresponding to the features of the object;providing a second region associated with the first region; wherein thefirst region comprises frames of reference for the set of objects withrespect to which the measurements are represented; and wherein, in thesecond region, the order of the object features is represented incorrespondence with the measurements represented in the first region,and representing the measurements in a corresponding frames ofreference, in conjunction with respective representations of the orderof the measured objects.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1a shows a conventional shaft.

[0014]FIG. 1b is a frequency plot of a range of diameters of the shaftof FIG. 1a showing the range of capability of a lathe producing theshafts, and the range of tolerances, according to prior art.

[0015]FIG. 2a is a top-view of an assembly of a shaft and its sleeve.

[0016]FIG. 2b is a frequency plot of a range of diameters of the shaftof FIG. 2a showing an upper specification level and a lowerspecification level.

[0017]FIG. 2c is a cross-sectional view of the assembly of FIG. 2a.

[0018]FIG. 2d is a side view of the sleeve of FIG. 2a.

[0019]FIG. 2e is a side view of a defective shaft.

[0020]FIG. 2f is an enlarged view of the defective shaft of FIG. 2eshowing various forms, in an embodiment of the present invention.

[0021]FIG. 3a is an isometric view of a shaft showing a defectivecross-sectional area, according to the present invention.

[0022]FIG. 3b shows a hierarchic arrangement of a category of geometricelements, or forms, in an embodiment of an aspect of the presentinvention.

[0023]FIG. 4 is a flow diagram showing an embodiment of a methodaccording to the present invention for diagnosing causes of defects inthe manufacture of a shaft.

[0024]FIG. 5 is a flow diagram showing an embodiment of a methodaccording to the present invention for diagnosing causes of defects in amanufacturing process.

[0025]FIG. 6a shows an arrangement of geometric forms and reproductiveforms, in an embodiment of the present invention.

[0026]FIG. 6b shows a shaft and its housing.

[0027]FIG. 7a is an isometric view of an engine block deck.

[0028]FIG. 7b is a graph of the distribution of measurements associatedwith surface profile of the engine block deck of FIG. 7a, in anembodiment of the present invention.

[0029]FIG. 7c is an isometric view of the engine block deck of FIG. 7ashowing a definition of geometric forms as points measured with respectto the vertical dimension of the block and line segments defined by aset of points according to the present invention.

[0030]FIG. 7d is an isometric view of the engine block deck of FIG. 7ashowing a definition of geometric forms as line elements, in anembodiment of the present invention.

[0031]FIG. 7e is an isometric view of the engine block deck of FIG. 7ashowing a definition of geometric forms in the form of pass elements inan embodiment of the present invention.

[0032]FIG. 7f is a multi-form chart, comprising a combination of amulti-form graph and a multi-form table showing the plot of the variouselements, or geometric forms, that constitute the engine block deck ofFIG. 7a, in an embodiment of the present invention.

[0033]FIG. 7g is a generalized multi-form chart of FIG. 7h representedin polar coordinates.

[0034]FIG. 8a is a condensed chart showing a hierarchical arrangement ofthe forms of the engine block deck of FIG. 7a.

[0035]FIG. 8b shows the finding of an exemplary defect in one of theforms used in a graphic analysis of FIG. 7f.

DETAILED DESCRIPTION

[0036] The present invention provides a diagnostic method for detectingdefects in a manufacturing process through an ability to control theprocess of creating shapes in a workpiece. A workpiece compriseselements, which may be portions and features, which are characterized byrespective geometric forms. The method, broadly speaking, isaccomplished through characterization of the manufacturing process,specifically characterizing the manufacturing process as a plurality ofaspects or steps that correspond to actions involved in forming of thevarious elements of a work product. Then, actions of the manufacturingprocess associated with work product defects are identified. Where themanufacturing process involves forming a piece of hardware, an elementof a workpiece may be a portion or feature of the workpiececharacterized by a geometric form. Through a systematic and preferably(though not necessarily) hierarchically ordered set of measurements ofthe elements of an apparently defective product, one or more defectiveforms associated with the actions of the manufacturing equipment on theworkpiece can be detected. In this manner, the source of a defect may bemore efficiently and directly arrived at, and corrective action may morereadily be taken at the point of occurrence of the defect.

[0037] According to an aspect of the present invention, a method foridentifying geometric forms for a workpiece that is acted upon bymanufacturing equipment begins by characterizing the process steps usedin producing that workpiece or product. For this purpose, a flow diagramis constructed. Corresponding to each process step (that is,corresponding to each action of the machine tool) in the process flowdiagram, a corresponding physical form of an aspect of the workpiece isidentified and diagrammed. A practitioner may find it advantageous tobegin this exercise with the least complicated geometric form that,together with successively higher order forms, identify the overall therelevant geometry of the workpiece. A form may, for example, be a set ofpoints that define radii of a shaft, a set of radii that together definean arc of the shaft, a plurality of arcs that form circles (or closedcurves, at any rate), and the set of circles that define the shaft, or asegment of it. Any variance of the actual workpiece data correspondingto a form, relative to a limit imposed by a specification, also referredto here as a reference datum, may provide evidence of a correspondingworkpiece defect, the cause of which may be an aspect of the processstep associated with that workpiece form. The overall variance of actualmeasurements from a datum can be distributed equally between theselected process steps, or allocated according to the expected influenceof the forms on the functioning of the workpiece. However, no one formshould be allocated more than 50% of the variance.

[0038] Accordingly, the geometric forms are measured. They may include,without limitation, radii, arc, closed curves (such as circles,ellipses, etc.) and surfaces. For each selected form, deviation of theallocated variance from the datum is computed. The form having thegreatest degree of deviation is postulated to be associated with adefect responsible for causing the unacceptable variance from the datum.A defect, if of sufficient severity, may give rise to an alertcondition. An alert conduction can be any condition recognized for themanufacturing process as one that may trigger an observation or otherresponse from an entity with responsibility for at least some aspect ofthe process. An alert condition may be inferred, for example, if adeviation exceeds a defined threshold based on a preselected rule. Therule may vary depending upon the characteristics of the form. Forexample, for an arc, the rule may state the limits of the angle thatsubtends the arc. Attention can then be focused on the errant processstep causing the unacceptable deviation, and an appropriate adjustmentidentified and implemented. Following one or more iterations of theadjustment process, the tendency of the machine tool to generate thedetected defects can be remedied.

[0039] Aspects of an embodiment of a method according to the presentinvention are shown in FIGS. 2a-2 f, in an example involving a malformedcylindrical shaft. FIG. 2a shows a top view of an assembly of shaft 100in sleeve 110. The shaft and the sleeve are separated from one anotherby clearance 120. The nominal bore diameter of the sleeve is D 115,while the nominal diameter of the shaft is d 105. Acceptable ranges ofdiameters 105′ and 115′, within a set of specifications, are plotted inFIG. 2b. A lower specification level (LSL) 103, and an upper levelspecification (USL) 107 are shown schematically in the same FIG. 2b. Across-sectional view of the shaft and sleeve are also shown in FIG. 2cfor clarity. The shaft has a base 109, and both the sleeve and the shafthave the same length l 125.

[0040]FIG. 2d shows a side view of sleeve 110, with shaft 100 withdrawnfrom the sleeve. The shaft itself is shown in FIG. 2e with its axis ofrevolution 104. FIG. 2e also shows a second shaft superimposed on thefirst shaft. Second shaft 140 is “out of true” at its free end oppositethe base, that is, slightly out of shape as manufactured, thoughexaggerated in the drawing for illustrative purposes. Its axis ofrevolution is denoted as 144, and the shaft has a diameter d′ 145.Measured along their respective axis of revolution, the diameter of bothshafts, namely, d and d′ fall within the specified tolerances and theirlengths are the same. This is shown in FIG. 2e by superimposing thedistribution of diameters of FIG. 2b along the extended axis ofrevolution 144 of shaft 140.

[0041] Having met the upper limit and lower level specifications, bothshafts, therefore, are expected to pass quality control. At the sametime, however, it is evident from FIG. 2e that, when shaft 140 isinserted into sleeve 110, it is not expected to rotate freely, as the“bent,” or defective, portion of the shaft will be contacting the insidewall of the sleeve.

[0042]FIG. 2f shows an exploded isometric view of defective shaft 140.Examination of the shaft reveals that the radius form R 153 and the arcform S 155 in the plane of each of the circles C 150 are “true” withintheir respective specifications. Although all the forms, up to andincluding the circle form, meet their respective specifications, thecylinder form 140, generated by the repetitive action of a machine tool,such as a lathe, is out of true, its axis of revolution lying along 144shown in FIG. 2f and not along axis 104. This condition requires acorrective action to adjust the action of the machine tool. Without acorrective action, the parts will not function properly, even thoughthey will meet the overall quality control specifications as depicted inFIGS. 2b and 2 e.

[0043] A need for corrective action can arise at any one of the stepsdescribed above. FIG. 3a shows another example of a defective shaft 300,a true cylinder with a straight axis of revolution 310, but also havinga radius 301, which deviates beyond a threshold datum. Shownschematically in FIG. 3a, R has a nominal value, and R1 and R2 deviatesubstantially from that datum. At this point, the machine is adjustedbefore proceeding further with the production of the workpiece. Oncethis corrective action is taken, then other forms can be examined in aniterative manner until the entire defect-causing process steps areremedied.

[0044] In one embodiment, shown in FIG. 3b, geometric forms at each stepare grouped together such that the same forms at a given step, whentaken together constitute the next form, in a hierarchical fashion.Thus, radii 301, constitute the next higher order arc form 302. Allradii 301 inscribe the same arc 302. Then, arcs taken togetherconstitute circles, and circles together define a cylinder or shaft. Theforms are shape elements, which together constitute more complex shapes.It is the difference, or deviation Δ, of the measured values of theforms from a reference datum at a given step that triggers an alertcondition to which attention must be given. Accordingly, the processstep corresponding to the form whose deviation gives rise to the alertcondition that must be adjusted to eliminate that alert condition.

[0045] An embodiment of a method according to the present inventionapplied to the fabrication of a mechanical shaft is shown in the flowdiagram of FIG. 4. A set of forms for a shaft in the same Figure isidentified in step 400. The forms are the radius, arc, circle andcylinder. The data from which the forms are generated are identified405. Then the form is set to that which is lowest in hierarchy 407, andthe form is selected 410 (radius, in this case). Starting with the firstselected form, three radii are measured at random (steps 420-440). Acharacteristic value, such as an average, μ, of the three radii, is nextcalculated in step 450. Then, an absolute value of the differencebetween the characteristic value, μ_(avg.) and a given reference datum,or μ_(datum), is calculated. In step 460, the deviation of thecharacteristic value from the datum is compared with a threshold value.If the deviation is greater than the threshold value, then an alertcondition 470 is declared. Consequently, the process step correspondingto the selected form, is adjusted at 480 and a new set of radiimeasurements is made (following steps 420-470) in an iterative fashionuntil alert condition is remedied.

[0046] When there is no alert condition, a second set of forms isselected at step 490 by incrementing to next form in hierarchy 495, andreturning to step 410. In the example shown in FIG. 4, threemeasurements are made for the arc form, S. Then, steps 420-460 arerepeated. If the deviation for the arc measurements exceeds a thresholdvalue, step 470, then the action of the machine corresponding to theproduction of the form is adjusted accordingly at step 480. The processis continued iteratively for circle and cylinder forms untilmeasurements for all forms are completed, any alert condition remedied,and until no further adjustment of the process machine is needed 500. Atstep 510, the machine is ready to produce forms according to a shopprint, and, consequently, the workpiece should be defect-free.

[0047]FIG. 5, which shows steps 600-710, is a generalization of theprocess steps of FIG. 4, where there are N forms that make up aworkpiece, or a product. A category of geometric form 600 comprises, ingeneral, a curvilinear segment, a closed curve, or a surface. Anothercategory can comprise spatial forms or temporal forms. The latter formsrepresent reproductive elements within which at least portionscomprising geometric forms of a workpiece can be reproduced repeatedlyand faithfully from location to location on a factory floor, or over atime interval of hours, days, or weeks.

[0048] In similar steps of FIG. 4, data from which the forms aregenerated are identified 605. Then the form is set to that which islowest in hierarchy 607, and the form is selected 610. Starting with thefirst of the N forms, first measurement of first set of forms isperformed 620. Second and third measurements are performed on the firstset of forms 630 and 640, respectively. A characteristic value is nextcalculated in step 650. Then, the difference between the characteristicvalue and a given reference, or datum, is calculated. In step 660, thedeviation of the characteristic value from the datum is compared with athreshold value. If the deviation is greater than the threshold value,then an alert condition 670 is declared. Consequently, the process stepcorresponding to the selected form, is adjusted at 680 and a new set ofmeasurements is made (following steps 620-670) in an iterative fashionuntil alert condition is remedied.

[0049] When there is no alert condition, a second set of forms isselected at step 690 by incrementing to next form in hierarchy 695, andreturning to step 610. Steps 620-660 are repeated. If the deviation forthe measurements exceeds a threshold value, step 670, then the action ofthe machine corresponding to the production of the form is adjustedaccordingly at step 680. The process is continued iteratively for theremaining forms until measurements for all forms are completed, anyalert condition remedied, and until no further adjustment of the processmachine is needed 700. At step 710, the machine is ready to produceforms according to a shop print, and, consequently, the workpiece shouldbe defect-free.

[0050]FIG. 6a shows a recast of the geometric forms 830 of FIG. 3b forillustrative purposes. Geometric elements, or forms, in the form ofshapes 850, form portions of, and the workpiece itself, such as theshaft shown in FIG. 6b. Reproductive forms, such as the locations wherethe shafts are made and the time intervals within which they are made,are all identified and assessed for alert conditions. The correspondingacts related to the manufacturing process are corrected to produce formsin accordance with a specified print to result in a defect free product.In order to achieve the reproducibility of a multiplicity of the sameshaft in a period of time 840, the same analysis as shown in FIG. 5 isextended temporally to account for deviations from a datum where Nincludes time as a form.

[0051] In one embodiment, a method for identifying defects through aprocess characterization approach according to the present invention isdescribed with reference to an example involving an automobile engineblock deck 900, shown in FIGS. 7a-7 h. The deck constitutes one-half ofan engine block. After the other half (not shown) is sealed and boltedon, the engine block is readied for operation. As detected duringoperation, the engine block leaks oil. The method according to thepresent invention is applied to find the defect, so that the necessaryadjustments to the machine tool that produced the engine block scan beappropriately adjusted to produce engine blocks that are defect free anddo not leak oil.

[0052] A specified flatness profile for the deck surface 910 shown inFIG. 7a is plotted as graph 930 in FIG. 7b. The existing flatnessprofile of the deck is as shown in graph 920 of the same Figure. Thedeviation of the existing surface profile from the required surfaceprofile well exceeds the upper speciation level (USL) 933 and the lowerspecification level (LSL) 935 as shown in the same FIG. 7b. In order toidentify the process step or steps causing the defective surfaceprofile, the various forms that constitute the deck are measured in ahierarchical order. The measurements are then subjected to a multi-formanalysis using a multi-form deviation chart. A multi-form deviationchart of the present invention uses a multi-vari graph with additionalfeatures that will be further described below

[0053] An examination of the block deck surface reveals that thesimplest measurable forms that constitute the surface comprise: 1) apoint on the surface, 2) line segments defined by a plurality of points,and 3) lines defined by line segments. Points 940 and line segments 950are shown in FIG. 7c. Lines 960 are shown in FIG. 7d, where at least twolines form a planar surface 910. The planar surface of the deck isformed by one pass of the machine tool in a single direction 970, and byanother pass 970 in the other direction, as shown in FIG. 7e. Oncehaving identified the forms to be measured, the measurements are madeaccordingly. The measurements are then represented in a multi-formdeviation chart as shown in FIG. 7f. The multi-form deviation chartcomprises a combination of a multi-form graph 980 and a multi-form table985 as shown in the same Figure.

[0054] In the illustrated embodiment shown in FIG. 7f, the multi-formdeviation chart comprises a multivari plot of the data. Three datapoints are preferred for each of the selected forms. The measured valuesare plotted in a multi-form graph 980. However, before making themeasurements, it is preferable that the selected forms are firsttabulated in multi-form table 985 presented with the multi-form graph asshown in FIG. 7f. The spatial relationship between multi-form graph 980and multi-form table can be contiguous or proximally adjacent. Thus,starting with one deck, two pass measurements are needed, since, atminimum, two passes are required to form one deck surface. Three linesconstitute one pass so that three lines are measured for each pass.Finally, three line segments are measured for each line. Lowest ordergeometrical form “points” 940 define the next higher order geometricalform “line segment” 950. However, in defining geometric form “line” 960,“line segments” 950 are lower order forms with respect to 960. Likewise,form “pass” 970 is constituted by three “line” forms. That is, pass 970occupies a higher order in the form hierarchy.

[0055] For multi-form analysis of additional engine block decks, themulti-form table and the accompanying multi-form graph are extendedlaterally L, and the measurements are repeated in exactly the samemanner as described above. A continuation for a second deck is shown inFIG. 7f. Furthermore, for multi-form analysis of additional forms, suchas for monitoring variations in decks manufactured at differentstations/locations on the same manufacturing floor, which may becharacterized as spatial variations, or for monitoring temporalvariations in decks manufactured in certain periods of time, such as agiven day, or week, the multi-form table can be extended vertically V toaccommodate the additional forms.

[0056] As shown in FIG. 7f, multi-form graph 980 and multi-form table985 are presented together to form a multi-form deviation chart.Preferably, deviations from a reference datum are represented by theaverage of the measured values in each category of form, although othermathematical relationships can be employed. FIG. 7f is constructed usingCartesian coordinates. Other frames of reference can also be used. Thus,in FIG. 7g, polar coordinates are used. In the same Figure, referencenumerals 900′, 940′, 950′, 960′, 970′ and 980′ correspond to the sameunprimed reference numerals of FIG. 7f. The space inside the solidboundaries represents the multi-form graph region, and the dashed spaceoutside the solid boundaries represents the region for placement ofordered forms. Additional ordered forms may be accommodated by expandingthe polar space outwardly, O. A condensed table having additional formsis shown in FIG. 8a. Lower order forms 980 are shown in boxes 990, whilehigher order forms 995 are shown below those boxes.

[0057] An analysis of the data plotted in a multi-form deviation chartmakes it possible to identify form(s) having the greatest variance, thatis, with the accompanying alert condition. The methods of the presentinvention show that non-random alert conditions generally are mostlikely to appear, if at all, in geometrical forms. On the other hand,random alert conditions, when they occur, are mostly found inreproductive forms, such as in reproduced workpieces themselves, or inspatial or temporal forms. Accordingly, the corresponding processstep(s) or action(s) of the manufacturing equipment is (are) adjusted.This is shown in FIG. 8b, where for illustrative purposes, a profiledefect of about 0.48 mm is found in a line form comprising lower orderline segment forms. Consequently, the process step (the action of amilling machine, for example) responsible for milling lines/linesegments is adjusted accordingly so that the ensuing engine blocks arefree of the previously detected defect, and no longer leak oil.

[0058] While the invention has been shown and described with referenceto particular embodiments, those skilled in the art will understand thatvarious changes in form and details of the methods according to thepresent invention may be made without departing form the spirit andscope of the invention.

What is claimed is:
 1. A method for diagnosing a cause of deviation froman intended form in a workpiece produced by a manufacturing process, inwhich at least one form is defined for the workpiece and manufacturingequipment acts upon the workpiece according to the manufacturing processto impart the form, the method comprising the steps of: defining aplurality of measurements for the workpiece, each relative to arespective reference datum; taking the defined measurements for theworkpiece; generating a record of the measurements; comparing therecorded measurements for each workpiece; and inferring from thecomparison of the measurements the existence of an alert conditionassociated with the action of the manufacturing equipment on theworkpiece.
 2. The method according to claim 1, wherein the at least oneform comprises a shape of at least a portion of the workpiece.
 3. Themethod according to claim 1, further comprising the step of plotting atleast a subset of the recorded measurements in a graph prior to the stepof inferring the existence of an alert condition.
 4. The methodaccording to claim 1, wherein the measurements correspond to ahierarchic set of forms characterizing the workpiece, each formcorresponding to an action of the manufacturing equipment.
 5. The methodaccording to claim 4, wherein the hierarchic set of forms comprises oneselected from the group consisting of a point form, a path segment form,a path form and a surface form.
 6. The method according to claim 4,wherein the hierarchic set of forms comprises two categories: a firstcategory of forms characterizing the shape of a portion of theworkpiece, and a second category of forms characterizing sets ofportions of the workpiece.
 7. The method according to claim 6, whereinthe sets of portions of the workpiece comprise repeating portions. 8.The method according to claim 3, wherein the graph depicts deviations ofthe measurements from respective reference data.
 9. A method foridentifying evidence of deviation from specification in a form producedin a workpiece by a manufacturing process, the manufacturing processbeing performed by respective manufacturing equipment, the methodcomprising the steps of: identifying a set of measurable formsassociated with the workpiece, each form corresponding to an action ofthe manufacturing equipment; for each form, identifying a referencedatum; for each form, making a set of measurements of the form relativeto the respective datum; comparing each set of measurements to arespective target range of values; and based on the comparison,inferring the existence of evidence of an alert condition.
 10. Themethod according to claim 9, wherein the form comprises a shape of atleast a portion of the workpiece.
 11. The method according to claim 9,wherein the measurements relate to a hierarchic set of formscharacterizing the workpiece, each form corresponding to an action ofthe manufacturing equipment on the workpiece.
 12. The method accordingto claim 9, wherein the hierarchic set of forms comprises twocategories: a first category of forms characterizing the shape of aportion of the workpiece, and a second category of forms characterizinga set of portions of the workpiece.
 13. The method according to claim12, wherein the sets of portions of the workpiece comprise repeatingportions.
 14. The method according to claim 9, further comprising thestep of inferring from the evidence an alert condition for thedeviation.
 15. The method according to claim 9, comprising the furtherstep of storing the measurements in a computer data storage device. 16.A method for identifying evidence of deviation from specification in aworkpiece produced by a manufacturing process, the manufacturing processbeing performed by respective manufacturing equipment, the methodcomprising the steps of: identifying a set of repeated portions of theworkpiece, each instance of a repeated portion having a form, the formof one instance of a repeated portion being substantially similar to theform of the other instances; for each instance of the repeated portion,making a set of measurements of the reproducible part relative to arespective reference datum; comparing each set of measurements to arespective target range of values; and based on the comparison,inferring the existence of evidence of deviation from specification. 17.The method according to claim 16, further comprising the step ofinferring an alert condition based upon the evidence of a preselectedrule.
 18. The method according to claim 17, wherein the preselected rulecomprises the deviation exceeding a threshold value.
 19. The methodaccording to claim 16, wherein at least a pair of instances of therepeated portion are contiguous in the workpiece.
 20. The methodaccording to claim 16, wherein the form comprises a shape of at least aportion of the workpiece.
 21. The method according to claim 16, whereinthe measurements relate to a hierarchic set of forms characterizing theworkpiece, each form corresponding to an action of the manufacturingequipment.
 22. The method according to claim 21, wherein the hierarchicset of forms comprises two categories: a first category of formscharacterizing the shape of a portion of the workpiece, and a secondcategory of forms characterizing one or more portions of the workpiece.23. The method according to claim 16, wherein the evidence of thedeviation is a basis for indicating an alert condition.
 24. The methodaccording to claim 23, wherein the alert condition is based uponapplication of a preselected rule to the evidence.
 25. The methodaccording to claim 24, wherein the preselected rule comprises adeviation exceeding a threshold value.
 26. The method according to claim16, comprising the further step of storing the measurements in acomputer data storage device.
 27. A method for assessing a condition ofa workpiece acted upon by manufacturing equipment, comprising the stepsof: identifying a set of forms, each form corresponding to an aspect ofthe action of the manufacturing equipment upon the workpiece; for eachform, making a plurality of measurements; for each plurality ofmeasurements, computing a respective deviation from a correspondingdatum; defining a deviation threshold; and if a computed deviationexceeds the deviation threshold, inferring the existence of thecondition attributable to the action of the manufacturing equipment onthe workpiece associated with action corresponding to the form for whichthe deviation exceeds the threshold.
 28. The method according to claim27, wherein the condition comprises an alert condition.
 29. The methodaccording to claim 27, wherein the plurality of measurements comprisesat least three measurements.
 30. The method according to claim 29,wherein the at least three measurements comprise exactly threemeasurements.
 31. The method according to claim 27, wherein the set offorms comprises two categories: a first category of forms thatcharacterizes a geometric element of a portion of the workpiece, and asecond category of forms that characterizes differences betweenworkpieces.
 32. The method according to claim 31, wherein the firstcategory of forms comprises one selected from the group consisting of apoint form, a path segment form, a path form and a surface form.
 33. Themethod according to claim 27, further comprising the step of plottingthe plurality of measurements for the plurality of forms on a singlegraph, prior to determining whether any computed deviation for each formexceeds a preselected threshold.
 34. The method according to claim 33,wherein the graph comprises a representation of each plurality ofmeasurements.
 35. The method according to claim 33, wherein the graphcomprises a representation of each plurality of measurements in relationto a respective form among a hierarchy of forms characterizing theworkpiece, each form corresponding to an action of the manufacturingequipment.
 36. The method according to claim 35, wherein the hierarchicset of forms comprises two categories: a first category of formscharacterizing the shape of a portion of a workpiece, and a secondcategory of forms characterizing one or more portions of the workpiece.37. The method according to claim 33, wherein the single graph comprisesa geometric deviation chart.
 38. The method according to claim 37,wherein the geometric deviation chart comprises a first region forcomparing measurements corresponding to the hierarchic set of geometricforms, and a second region contiguous with the first, for recording thefrequency of repetition of the forms that comprise portions of theworkpiece.
 39. A method for detecting deviations from an intended formin a mechanical part, the deviations based upon computed differencesbetween measured geometric properties with respect to a reference datumand defined threshold values, the deviations from an intended formcaused by a machine tool operating on the mechanical part, the methodcomprising the steps of: a. identifying a hierarchic set of geometricforms characterizing the mechanical part, each form corresponding to anaction of the machine tool on the part; b. categorizing the geometricforms from a lowest order to a highest order; c. making a plurality ofmeasurements corresponding to the lowest order form, each plurality ofmeasurements made relative to a reference datum; d. computing deviationsbased on differences between the plurality of measurements and thereference datum; e. comparing the deviations with respective thresholdvalues, the deviations exceeding threshold values indicating an alertcondition; and f. if an alert condition is present, inferring adeviation from the intended form.
 40. The method according to claim 39,wherein if no alert condition is present, performing the steps c-f for ahigher order geometric form.
 41. The method according to claim 39,wherein the hierarchic set of geometric forms comprises two categories:a first category of forms characterizing the shape of a portion of aworkpiece forming the mechanical part, and a second category of formscharacterizing one or more portions of the workpiece.
 42. The methodaccording claim 41, wherein the first category of geometric formscomprises at least one selected from the group consisting of a segment,a line and a plane.
 43. The method according to claim 41, wherein thefirst category of geometric forms comprises at least one of the groupsconsisting of curvilinear segment, a closed curve and a surface.
 44. Themethod according to claim 41, wherein the second category of geometricforms comprises a surface defined by forms selected from the firstcategory of shapes.
 45. The method according to claim 39, wherein thestep of checking for an alert condition is performed by plotting theplurality of measurements on a geometric deviation chart.
 46. The methodaccording to claim 45, wherein the geometric deviation chart comprises afirst region for comparing measurements corresponding to the hierarchicset of geometric forms, and a second region contiguous or adjacent thefirst, for representing the frequency of repetition of the forms thatcomprise portions of the workpiece.
 47. A method for characterizing theability of a machine tool to reproduce a product without deviating froma specification intended for at least a portion of the product, thecharacterization based upon taking geometric measurements, the methodcomprising the steps of: a. identifying a set of geometric forms presentin the product; b. selecting a first of the set of geometric forms; c.making a plurality of measurements corresponding to the selectedgeometric form; d. for each plurality of measurements, computing adeviation from a respective reference datum; e. checking for an alertcondition based on each of the respective deviations; f. if an alertcondition is present, adjusting the machine tool and repeating themethod from step c iteratively until no further alert condition isfound; and g. if no alert condition is detected, repeating the methodfrom step b and incrementing to the next form until all geometric formshave been selected.
 48. The method according to claim 47, wherein afirst category of geometric form comprises at least one selected fromthe group consisting of a segment, a line and a plane.
 49. The methodaccording to claim 47, wherein the geometric form comprises a surfacedefined by forms selected from the first category of geometric form. 50.The method according to claim 49, wherein the first category ofgeometric forms comprises at least one of the groups consisting ofcurvilinear segment, a closed curve and a surface.
 51. The methodaccording to claim 47, wherein the specification comprises at least oneof the groups consisting of a spatial form and a temporal form.
 52. Themethod according to claim 51, wherein the spatial form comprisesphysical locations where the product is made.
 53. The method accordingto claim 51, wherein the temporal form comprises an interval of time.54. A method for representing in a physical recording medium measureddeviations for features attributable to the forming of a physicalobject, comprising the steps of: providing a data structure embodied inthe physical recording medium; identifying an order for the features;providing a first region for comparing measurements corresponding to thefeatures of the object; providing a second region associated with thefirst region; wherein the first region comprises frames of reference forthe set of objects with respect to which the measurements arerepresented; and wherein, in the second region, the order of the objectfeatures is represented in correspondence with the measurementsrepresented in the first region, and represents the measurements incorresponding frames of reference, in conjunction with respectiverepresentations of the order of the measured objects.
 55. The methodaccording to claim 54, wherein the second region is contiguous with thefirst region.
 56. The method according to claim 54, wherein the set ofobjects comprises forms having shapes of differing geometries.
 57. Themethod according to claim 54, wherein the set of objects comprisesspatial forms representing locations where the product is made.
 58. Themethod according to claim 54, wherein the set of objects comprisestemporal forms representing intervals of time.
 59. The method accordingto claim 54, wherein the frames of reference comprise Cartesiancoordinates.
 60. The method according to claim 54, wherein the frames ofreference comprise polar coordinates.